A band gap of a nitride compound semiconductor whose composition is expressed by the general formula InxGayAlzN (where x+y+z=1, 0≦x≦1, 0≦y≦1, 0≦z≦1) may have a size corresponding to blue light or ultraviolet light through adjustment of the mole fraction of each element. Therefore, there have been vigorous research activities directed to light-emitting devices, e.g., semiconductor lasers, that comprise a nitride compound semiconductor as an active layer.
FIG. 1 shows the crystal structure of a nitride compound semiconductor. As shown in FIG. 1, a nitride compound semiconductor has a crystal structure of a hexagonal-system. Therefore, when fabricating a semiconductor laser which is constructed so that its upper face (principal face) is the (0001) plane and its resonator end faces are the M-plane (1-100), cleavage is likely to occur not along an A-plane which is perpendicular to these planes, but along a crystal plane which is tilted by 30° from the A-plane. As a result, there is a problem in that, not only when performing cleavage along the A-plane, but also when forming cleavage along the M-planes (1-100) to form the resonator end faces, miscleavage (end-face cracks) is likely to occur in a direction which is tilted by 60° from the M-plane (1-100).
Due to this problem, it has conventionally been very difficult to fabricate a nitride compound semiconductor element having smooth resonator end faces.
A sapphire substrate, which has conventionally been widely used as a substrate for nitride compound semiconductor elements, is not capable of cleaving. Therefore, when forming a semiconductor laser having a sapphire substrate, it has been practiced to perform scribing along the M-plane from the side of a nitride compound semiconductor layer that is grown on a sapphire substrate to thus form a scratch in the nitride compound semiconductor layer, this being an attempt to facilitate the formation of a cleavage plane.
Patent Document 1 discloses a method which involves performing an edge scribing for a nitride compound semiconductor layer, and thereafter performing a cleavage through breaking.
Similarly in the case of cleaving a semiconductor laser comprising a GaN substrate, which is being used in the recent years, it has been practiced to form scribing grooves along the M-plane from the side of a nitride compound semiconductor layer that is grown on the GaN substrate, this being an attempt to facilitate cleavage. Patent Document 2 discloses a method of, after linearly forming scribing grooves in a nitride compound semiconductor layer, performing a cleavage through breaking.
[Patent Document 1] Japanese Laid-Open Patent Publication No. 2000-058972
[Patent Document 2] Japanese Laid-Open Patent Publication No. 2003-17791